1. Field of the Invention
This invention relates to a method of connecting a wear-resistant copper alloy to a synchronizer ring (sometimes simply called as "a synchro" for short) body made of an iron material as a sliding member and which is adapted for use in transmissions of vehicles and the like.
2. Description of the Prior Art
Synchronizer rings solely made of a copper alloy are in general use. However, the recent increase of power and torque in passenger cars or the recent use of high power gear shifts with hydraulic servo units in large-sized vehicles such as trucks, buses and the like applies a larger load to the synchronizer ring so that a synchronizer ring made solely of a copper alloy has become insufficient in the wear resistance of a chamfering hob therein or in the whole rigidity and strength thereof since a high load is applied thereto at the time of shifting gears although it is sufficient in wear resistance at the sliding surface thereof.
Accordingly, there have been three kinds of heavy-duty synchronizer rings, each having a wear-resistant part bonded to the sliding portion thereof as follows:
(1) A synchronizer ring in which an iron material is spray-coated with Mo.
(2) A synchronizer ring in which an iron material is coated with a resin (e.g. phenol resin)
(3) A synchronizer ring in which a wear-resistant material is mechanically bonded to an iron material.
The method (1) which is widely employed by large-sized vehicles etc. causes a high cost since the sliding material Mo is very expensive.
The method (2) generates a change depending on the temperature of use in synchronizing performance that is most important to the synchronizer ring. Under some conditions of use, the sliding surface of the synchronizer ring sometimes instantaneously becomes over 300.degree. C. to melt the resin so that the function of the synchronizer ring is liable to deteriorate. On the other hand, when it is used at a low temperature, the lubricant oil becomes so viscid that it cannot be removed from the sliding portion completely, prolonging the period for synchronization and generating gear noise. As a result, the available range of temperature is limited.
Methods of fixing the sliding material to the ring body by way of screws and caulking are known in method (3).
FIG. 7 shows how to bond a Borg-Warner synchronizer ring body 21 and a member having a sliding surface (referred to as a sliding member hereinafter) 22 to each other by way of a screw 23. This method, however, has a problem in mounting strength due to the mechanical bonding and it is obvious that it is disadvantageous in cost since it requires a large number of parts and assembling processes, and the strict quality control and dimensional accuracy of each part. Moreover, since the screw mounting portion has no sliding material, it is difficult to secure a contact area thereon, so that it is disadvantageous in performance. Furthermore, it is very difficult to attach the sliding member 22 to a synchronizer ring having a small diameter. In FIG. 7, denoted at 24 is a hub sleeve and 25 is a gear cone.
FIG. 8 shows a method of bonding a pin synchronizer ring 26 and a sliding member 27 to each other by way of caulking protrusion 28. A copper alloy material which can be used for caulking is generally made having a low rigidity for securing ductility so that it is liable to be inferior in wear resistance, and deemed to have no sufficient synchronous performance.
Moreover, caulking is classified into press fitting, shrink fitting and expansion fitting, among which press fitting causes seizure or galling at the time of engaging one in the other. On the other hand, shrink fitting and expansion fitting are liable to cause the drop off of the sliding member from the ring body when the working temperature becomes high or low since they take advantage of elastic deformation accompanied by thermal expansion or thermal contraction for bonding. Furthermore, since all of the above three methods bond them to each other in a state wherein one is engaged in the other, interference is as short as 3/100 of the diameter at the most, so that securing dimensional accuracy requires a precision machining at a high cost. Still furthermore, since they can be separated by a small force, these methods are not adapted for large-sized vehicles which generate a large torque.
There is another method of bonding wear resistant materials to the ring body by way of brazing. Since temperatures often reach a high temperature of over 600.degree. C. at bonding portions in brazing, the ring body is liable to distort to cause a precision problem. It is also very difficult to work with hands in a limited space of a synchronizer ring.
The present invention has been made from the problems set forth above to provide a synchronizer ring of heavy duty operation and high performance by bonding a specially selected wear-resistant copper alloy material to the sliding member of the ring body by way of hot working.